Once a NOTAM is issued, it is no longer a hazard alert, but you are still entitled to the NOTAM under ATC initiated FIS - "will include the provision of pertinent operational information" This should be provided to aircraft within 1 hours flight time at the time the NOTAM is issued.
MATS (instructions for ATC) says:
Aircraft to notify
Notify aircraft, at the time operational information and the existence of non-routine MET products is identified:
a) except for amended ARFOR, by directed transmission to those aircraft maintaining continuous communication and within one hour’s flight time of the conditions (two hours in the case of SIGMET);
b) where continuous communication is not required, by broadcasting on appropriate ATS frequencies to those aircraft that could be within one hour’s flight time of the conditions (two hours in the case of SIGMET); and
c) by directed transmission to all affected aircraft engaged in SAR action.